Stainless steel process



' eral operational steps,

/ is indicated in the claims.

, equipment, and the like.

Patented Nov. 1944 John N. Lynn,

Iron and Steel Corporation, corporationfof Delaware Towson, MIL,assignor to Rustless Baltimore, Md., a

" No Drawing. Application July '31, 1,941, Serial No.404,919

The present invention relates to tents, and particularly to anartofheattreating and working the same. I

One of the objects of my invention "the pro- "vision of a simple, directandpractical process for improving the cold-working, properties ofhigh-chromium stainless steel alloys of high-carbon contents, whichenables the employment Fof conventional equipment at maximum efilciencyand with minimum.expense.

-. Another object of my invention is the coldreduction, of stainlesssteel bars, rods and wire, of the class indicated, inaneconomical'manner of the same to one described herein, the

To promote a clearer understanding of my invention, it is to be noted at,thispointlthat the hardenable hypereutectoid, high-chromium' stainlesssteel alloys comprising" 16%"to 22% chromium, 0.75% to 1.5%carbon, andthebalance substantially iron, except for special purposes, smalladditions'of molybdenum and the like, are metals of great'strength,toughness and hardness, possessing high resistance to corrosion andabrasion. Because of excellentserviceability, thesealloys enjoy a widerange of utility,

applications as the procutlery, valves, valve being employed in suchduction of ball bearing 1 seats, dental instruments, superheated steamparts, milk bottling equipment, oil ing machines, laundry pumps,sprayequipment, chemical Alloys of the class described, however, have,as the result of hot-working, objectionable brittleness, which conditionpersists even where the metal is annealed after hot-working. Beforecold-drawing, a high-carbon, high-chromium stainless steel into rods orwire, for; example, it

is conventional practice to hot-roll the metal us and in after, themetal is exposed' alternately toa'nneal ing, pickling and cold-drawingfoperatio'nsuntil the metal is drawn 'torods or '7 Claims. (01. 14s 12)high-chro-. mium stainless steel alloys of, high-carbon con-' throughfanfinitial range of reduction." There- 1. Much difliculty. is,encounteredgin'the form of f breakage during. the cold-drawing. steps,because of metal brittleness incurredby hot-rolling. Cold-drawing ofhigh -carbon,,,high-chromium stainless steel alloys in accordance withprior praotice,'-';therefore, is tedious.

often is found with finished metal'productscbe- -cause they containflaws, have-irregular grain the' hotrolling temperature, to beobiectionably brittle.

ability. e

structure and lack strength, toughnessand dur- Although I do not care tobe bound by an ex- 4 planation,'itappears that partof the carbon inhypereutectoid stainless steels is in solid solution with ironandchromium, while anotherpa'rtJis in the metal carbide form. When-Ianalloysteel of the class described isihot-rolled,-car-bide particlessegregate in the metal'to disrupt uniformity ofthe metal grain"structure. I Upon coolingfrom the metaljis found previous practice,annealing of the hot-rolled metal at, 1500 to 1600 F. serves to softenthe metal andto relieve stresses incurred by hotthe presence of carbideH culty is encountered in i into rodsand wire, as b rolling. Infs'piteof the annealing operatlomdifll- .cold-workin'g' the metal y drawing,becausefofits excessive brittleness and lack of uniform grain structure.Aftercold-working the metal, ,grain structureis not unifor segregation;The resultant rod or wire'products are not entirely uniform in strength,toughness, hardness, corrosion resistance and abrasion resistanc i r Anobject of my invention,- accordingly,'is the provision of a process forproducing high-carbon,

high-chromium stainless steel products of im- 7 proved cold-working andcold-forming properties steel barsQrods and wire ofa and'especially ofproducing cold-drawn stainless ensuring a minimum amoun of breakage and"waste in the cold drawing.

Referring now more tice of my invention, I improve the cold-workingproperties of high-carbon, high-chromium stainless steels by aheat-treatment cofn'prising suc- {cessive quench-hardening and annealingoperations, respectively; To effect ahardening of the metal, I heat itto a temperature high enough to T Dims v time-consuming, andconsequently,'uneconomical. Moreover, fault In accordance withapparently because of uniform structure partieularlyto the prac remaindispersed in 2 aeeaase ensure, within practical limits, that a maximumbreakdown of carbide striations occurs; after which,'I cool the metalrapidly in oil, wateror air.

:Following these operations, carbides are found to exist in welldispersed globular form interspersed in a uniform and refined grainstructure. I then anneal the metal by heating it through the criticalrange and thereafter slowly cooling it back through the critical range.Annealing does not destroy the effect of thorough metal carbidedistribution brought about by'the previous hardening operation. It does,however, considerably soften the steel to permit subsequent ready coldworking or cold-forming. It can be cold-worked more readily than steelsheat-treated in accordance with practices heretofore employed inthe,

art. Moreover, the grain is more uniform and there is very much lessbreakage in the coldworking operation.

As illustrative of the practice of my invention,;

I heat a coil of stainless steel rod material analyzing 16% to 22%chromium, 0.75% to 1.5% car-. bon, and the balance iron, to atemperature prefand of uniform quality. A minimum number of breaks occurlri'the drawing.

For example, in drawing hot-rolled rod stock of /uinch diameter, andanalyzing 17.0% chro mium, 1% carbon and the remainder iron. into wireof 0.284 inch diameter, aflrst drawto 0.318 inch was employed with asubsequent annealing treatment. x In total reduction, the wire brokeonly three times. According to prior practice, as many as fifty breakscommonly are encountered. These, of course, result in delay and aproduct of inadequate length. Moreover, with prior methads, as many'assix to eight intermediate annealing operations arerequired, in orderto achieve a reduction of this consequence in such a stainless steel,while my process requires but one or two intermediate anneals. Moreover,my finished wire-is stronger, tougher, and more serviceablethanheretofore known'products because of imerably within the range of1800' F.'to 1925' II. At

*such temperatures, carbides break up, recrystallization occurs.

A metal soaking period of short duration at temperature, encourages-amore complete readjustment of the metal crystalline structure. At theend of the heating operation, I re-v move the metal from thefurnacewhile it is still at a temperature of 1800 F. to 1925 F. Themetal is quench-hardened promptly, Preferably by rapidly cooling in oil.

. ing in air may be effected. The hardened metal possesses n Wheredesired, quenchilne and uniform grain structure wherein metal carbidesare well dispersed and are in globular form.

While I do not wish to be limited specifically to the range oftemperatures given, Iflnd the microstructures of metal piecesquench-hardened from temperatures somewhat below 1800 F. contain bandedcarbides to some degree, while those quench-hardened from temperaturessubstantially above 1925 1. show grain growth. g

Following the hardening treatment, I anneal the hardened metal in aheat-treatment furnace, by heating it to a temperature of 1500 F. to1600' F. From this temperature, the metal is cooled slowly in thefurnace, preferably at a rate of approximately F. per half-hour, toabout 1200 F. from which it is air-cooled to room tempera- 'ture;

AnnealingQin this case, brings about a softening of the hard, uniformmetal. Carbides globular form. It can be seen, therefore, that thehardening operation is carried out primarily to lend refinement to theinvention -as applied proved grain structure.

Thus, it will be seen that'tbere has been provided in this invention-anart of working highchromium stainless steel alloys of high-carboncontents, by which the various objects hereinbefore noted, together withmany thoroughly practicaladvantages, are'successfully achieved. Also, itwill be seen that the heat-treatin aspect of my to high-carbon stainlesssteels of the class described, enables them to withstand variouscold-working and cold-forming operationssuch as straightening, bending,drawing, sectional reduction or-the like.

Aside from the many practical and economical operational advantages ofmy invention, coldworked products fashioned in accordance with myprocess are of-superior quality. They possess fine and uniform grainstructure; flaws, blemishes, tears andworking defects, accordingly,being-at a minimum. The products are tough. hard and strong, andpossessimproved resistance to corrosion and abrasion.

While as illustrative of thepractice of my invention, high-chromium,high-carbon stainless I 22% chromium and 0.75% to 1.5 carbon arespecifically described, good results are achieved in similar stainlesssteels, even where the chromium and carbon con. tents are extendedsomewhat.

' As many possible embodiments may be made of my invention and as manychanges may be made in the embodiments hereinbefore set forth, it will-be understood that all matter described herein isto be interpreted asillustrative, and not in a limiting sense.

metal, while the annealing oper'ationserves to soften the refined metal.I find the metal'to be far less brittle than if the hardening operationhad been omitted.

After my sequential hardening and annealing steps, I find the metal tobe in ideal conditionfor cold-working. In cold-drawing high-carbonstainless steel rods of the type'described into rods and wire, I subjectthe metal to alternate colddrawing and annealing operations until themetal is reducedto final form. Preferably, the annealing is conducted ina controlled non-oxidizing atmosphere; otherwise, the annealingtreatment is followed by a pickling operation to remove the anneal scaleprior to a further-cold-drawing op.- eration. The annealing operationsrelieve stresses inthe metal incurred by cold-working. The finishedmetal then is ready for additional treatment orready for particular use.It is of good length Y I claim: v

1. In preparing for cold-working a previously hot-worked hypereutectoidstainless steel containing at least 16% chromium and 0.75% carbon' whichis hardenable by' heat-treatment, the art which includes,quench-hardening the same from a temperature of l800 F. to 1925 F., andthen annealing the hardened metal at a temperature of 1500 F. to 1600"F.

2. In the cold-working of hot-worked highchromium hypereutectoid alloystainless steel of high-carbon content, comprising 16% to 22% chromiumand 0.75% to 1.5% carbon, the art which includes, quench-hardening saidmetal from a temperature of at least 1800 F., annealing the hardenedmetal at a temperature of 1500" F. to 1600 F., pickling the same, andcold-working said annealed andpickled metal.

3. In the production of a cold-drawn, high- .chromium hypereutectoidstainless steel alloy of high-carbon content comprising 6% to 22% F.,annealing the hardened 4. In the cold-working of hypereutectoidhotworked stainless steel comprising 16% to 22% chromium and 0.75% to1.5% carbon content, the steps which include, heatin the same in asuitable furnace to a temperature of 1800" F. to 1925 F. torecrystallize the metal, rapidly cooling the metal to harden the same,softening the metal by annealing it at a temperature of at least 1500F., and then cold-working the same.

5. In the cold-working of a hypereutectoid previously hot-workedstainless steel comprising 16% to. 22% chromium and 0.75% to 1.5%carbon, the art which includes, heating the metal in a suitable furnaceto a temperature of .1800 F. to 1925 F. and then rapidly cooling themetal to harden the same, heating the hardened metal in a suitablefurnace to a temperature of 1500 F. to 1600 F. and slowly cooling saidmetal to sub- 3 stantially 1200 F. to anneal the same, and coldworkingthe annealed metal.

6. In the production of cold-drawn hypereutectoid rod or wire-comprising16% to 22% chromium and 0.75% to 1.5% carbon, the art whichincludes,heating hot-rolled bar or rod stock in a suitable furnace to atemperature of 1800 F. to 1925 F., and rapidly cooling said stock toharden the same, reheating the hardened stock in a suitable furnace atatemperature of 1500 F. to 1600 F. and slowly cooling said stock tosubstantially 1200 F. to anneal the same, and

finally cold-drawing the annealed stock into rod or wire.

7. In the production of cold-drawn hypereutectoid rod or wire comprising16% to 22% chromium and 0.75% to 1.5% carbon, the art which includes,quenching hot-rolled bar or rod stock from a temperature of 1800 F. to1925 F., re-heating and annealing the stock at 1500 F. to 1600 F., andthereafter subjecting the annealed metal alternately to cold-drawing andannealing operations. I

JOHN N. LYNN.

